CINCINNATI -- The Mets are still mulling whether or not to allow Johan Santana to begin a Minor League rehab assignment this week.

The team expects to make a decision on Tuesday regarding Santana, who threw a 45-pitch bullpen session Sunday afternoon and could begin a rehab assignment on Wednesday.

"They probably talked down there," Mets manager Terry Collins said of Santana and his rehabilitation staff in Florida. "They haven't called me yet."

Once Santana does begin a rehab assignment, be it Wednesday or next week, he will have 30 days to work into game shape before the Mets must activate him. At worst, then, Santana is looking at an early-September return.

Undergoing surgery last September to repair a torn capsule in his left shoulder, Santana still has two guaranteed seasons remaining on the six-year, $137.5 million contract he signed in 2008. The Mets also hold a $25 million team option for the 2014 season, with a $5.5 million buyout.

When healthy, Santana has been quite successful for the Mets, posting a 40-25 record and a 2.85 ERA in 88 starts over the past three seasons.

Pagan out, undergoes tests for fatigue

CINCINNATI -- Mets outfielder Angel Pagan underwent testing on Monday to determine the cause of his recent in-game fatigue.

The team is awaiting results on the blood work of Pagan, who left Sunday's game in the fifth inning due to dizziness. Jason Pridie started in center field Monday evening in Pagan's place.

"For about a week now, in the middle of the game, he just starts to lose energy," Mets manager Terry Collins said. "We'll just give him a little checkup."

Pagan, who said Sunday that he does not consider the issue serious, is batting .232 with four home runs and 18 stolen bases in 71 games. He has drawn mild rumors as a possible trade target for contenders prior to Sunday's non-waiver deadline.